Presently, engine air valves are actuated by a cam shaft bearing on a poppet type valve stem and opening the valve by action of the eccentric cam lobe bearing on the valve stem acting counter to the bias of a closing valve spring. Closing of the valve is by means of the bias exerted by the valve spring.
The present design involves high mass, takes up significant space, and is limited in the amount of variation in valve opening and closing profile that may be achieved to increase performance and minimize pollutant generation over a wide range of engine operating conditions. There is a need in the industry then to reduce the mass of the valve train, minimize the space occupied by the valve train and increase the flexibility of the achievable variation of the valve opening and closing profile.